1. Field of the Invention
The present invention relates to an image recording apparatus using a plurality of diffraction grating type light modulator elements for recording an image on a recording medium.
2. Description of the Background Art
Developed has been a diffraction grating type light modulator element which is capable of changing the depth of grating by alternately forming fixed ribbons and moving ribbons on a substrate with a semiconductor device manufacturing technique and sagging the moving ribbons relatively to the fixed ribbons. It is proposed that such a diffraction grating as above, in which the intensities of a normally reflected light beam and diffracted light beams are changed by changing the depth of grating, should be used for an image recording apparatus in techniques such as CTP (Computer to Plate) as a switching element of light.
For example, a plurality of diffraction grating type light modulator elements provided in the image recording apparatus are irradiated with light, and then reflected light beams (zeroth order diffracted light beams) from light modulator elements in a state where the fixed ribbons and the moving ribbons are positioned at the same height from a base surface are guided to the recording medium and non-zeroth order diffracted light beams (mainly first order diffracted light beams) from light modulator elements in a state where the moving ribbons are sagged are blocked, to achieve an image recording on the recording medium.
In such a diffraction grating type light modulator element, however, since the driving voltage supplied for the moving ribbons and the amount of sag of the moving ribbons are not in proportion to each other, even if a curve indicating a change in driving voltage at the time when the light modulator element is changed from an ON state (a state where a signal beam is guided from the light modulator element to the recording medium) to an OFF state (a state where no light is guided from the light modulator element to the recording medium) is made equivalent (symmetrical) to a curve indicating a change in driving voltage at the time when the light modulator element is changed from the OFF state to the ON state, changes in intensity of light outputted from the light modulator element in both the cases do not become equivalent (symmetrical) to each other.
Specifically, when the light modulator element is changed from a state where the change in sag of the moving ribbons is large with respect to the change in driving voltage to a state where the change in sag is small, it is hard for the moving ribbons to follow the driving voltage since a large initial acceleration is given to the moving ribbons and this results in excessively quick moving of the moving ribbons and oscillation thereof. As a result, even if the light modulator elements are changed periodically between the ON state and the OFF state, it is hard to write appropriate dots on the recording medium which travels at constant speed relatively to the light modulator elements.
The present invention is intended for an image recording apparatus for recording an image on a recording medium by exposure, and it is an object of the present invention to achieve an appropriate image recording in consideration of the characteristics of a diffraction grating type light modulator element.
According to an aspect of the present invention, the image recording apparatus comprises a light modulator having a plurality of diffraction grating type light modulator elements with fixed ribbons and moving ribbons alternately arranged, a light source for emitting a light with which the light modulator is irradiated, a holding part for holding a recording medium on which an image is recorded with zeroth order diffracted light beams from some of the light modulator elements in which the moving ribbons do not sag, a transfer mechanism for transferring the holding part relatively to the light modulator, a detection circuit for detecting whether or not there is a transition of each of the plurality of light modulator elements from a state of emitting first order diffracted light beams to a state of emitting a zeroth order diffracted light beam, and a control circuit for temporarily supplying each of the light modulator elements on which the transition is detected with an auxiliary driving voltage between a driving voltage on emission of first order diffracted light beams and a driving voltage on emission of a zeroth order diffracted light beam.
The image recording apparatus of the present invention can suppress an overshoot of the moving ribbons and consequently achieve an appropriate image recording.
More generally, the detection circuit detects whether or not there is a transition of each of the plurality of light modulator elements from a state where the amount of sag of the moving reflection surfaces is large with respect to a change in driving voltage to a state where the amount is small.
The present invention is further developed into a technique to detect a state transition of each of the plurality of light modulator elements at a series of points in time and supply each of the light modulator elements with a driving voltage in accordance with the state transition at the series of points in time
This achieves a flexible control of the driving voltage.
The present invention is also intended for a method of recording an image on a recording medium by exposure.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.